Circuit board structure and method for manufacturing a circuit board structure

ABSTRACT

The present publication discloses a method for manufacturing a circuit-board structure. In the method, a conductor layer is made, which comprises a conductor foil and a conductor pattern on the surface of the conductor foil. A component is attached to the conductor layer and the conductor layer is thinned, in such a way that the conductor material of the conductor layer is removed from outside the conductor pattern.

The present invention relates to a method for manufacturing acircuit-board structure and a circuit-board structure.

The circuit-board structure manufactured can form, for example, part ofa circuit board, a multilayer circuit board, a component packet, or anelectronic module.

The circuit-board structure comprises at least one layer of conductorpatterns and at least one component, which is connected electrically tothe conductor patterns.

The invention also relates to methods, in which at least one componentconnected to a conductor pattern is surrounded by an insulation-materiallayer. Such solutions can be alternatively also referred to ascircuit-board or module structures, which contain buried, embedded, orbuilt-in components. The insulation-material layer surrounding thecomponent is typically part of the basic structure of a circuit-board ormodule structure, which forms a support for the innermost conductorlayers of the circuit board or module.

Application publication U.S. 2005/0001331 discloses a circuit-boardstructure manufacturing method, in which first of all a circuit board ismanufactured, which comprises an insulator layer and a conductor patternon top of it. After this, a semiconductor component is connected to theconductor patterns by means of a suitable flip-chip method. Theconnection takes place through contact bumps on the surface of thesemiconductor component. In the method of the US publication, after theconnection of the component a patterned and unpatternedinsulation-material layer is laminated on top of the circuit board and aconductor-pattern layer is further laminated on their surface.

Patent publications U.S. Pat. No. 6,038,133 and U.S. Pat. No. 6,489,685as well as application publication U.S. 2002/0117743 disclose a method,in which a conductor pattern is manufactured on the surface of adetachable membrane, and a semiconductor component is connected to theconductor pattern by means of a flip-chip attachment method. After this,the component is surrounded with a layer of insulation material and thedetachable membrane is removed.

The aforementioned publication U.S. Pat. No. 6,038,133 and U.S.2002//0117743 also disclose methods, in which a component is connectedby a flip-chip method not to conductor patterns but to a unifiedconductor foil, from which conductors patterns are formed in a laterstage of the process. Corresponding method are also disclosed, forexample, in the publications U.S. Pat. No. 5,042,145; WO 2004/077902; WO2004/077903; and WO 2005/020651.

In addition to the aforementioned types of method, many other methodsare known, which can be used to manufacture circuit-board structurescontaining components. The components can, for example, first of all beplaced inside an insulating-material layer and connected electrically tothe conductor layer only after this, as is disclosed in applicationpublication WO 2004/089048. In the method of application publication WO2004/089048, the component is glued to the surface of a conductor layerand, after the gluing of the component, an insulating-material layer,which surrounds the component attached to the conductor layer, is formedof attached to the conductor layer. After the gluing of the component,vias are also made, through which electrical contacts are formed betweenthe conductor layer and the contact areas of the component. After this,conductor patterns are formed from the conductor layer, to the surfaceof which the component is glued.

The invention is intended to develop a new method for manufacturing acircuit-board structure.

According to the invention, a method is implemented, in which aconductor layer is made, which comprises both a conductor pattern and aconductor foil. The component is attached to the conductor layercomprising the conductor pattern and conductor foil and, after theattaching of the component, the conductor layer is thinned, in such away that the conductor material of the conductor layer is removed fromoutside the conductor pattern.

In this way, a new method for manufacturing a circuit-board structure iscreated.

The invention has several embodiments, a few of which are presentedbriefly in the following.

The manufacture of the conductor layer can be performed in severaldifferent ways:

-   -   According to one embodiment, the conductor layer is manufactured        by growing a conductor pattern on top of a conductor foil, using        a growing method. Thus the conductor foil is grown directly into        its correct shape.    -   According to a second embodiment, the conductor layer is        manufactured by thinning areas of a thicker conductor foil, in        such a way that a thinner conductor foil and a conductor pattern        on top of this remain. The thinning of the areas can be        implemented, for example, using a photo-lithographic method, or        a laser-ablation method.

The attachment of the component can also be performed using severaltechniques and in one or more stages. The attachment of the component isconcerned with achieving a mechanical attachment between the componentand the conductor pattern, in such a way that the component and theconductor pattern will remain in place in the circuit-board structure.The attachment of the component is also concerned with making anelectrical contact between the component and the conductor pattern, insuch a way that, through the conductor pattern, the desired voltages andcurrents can be led to the component and away from the component. Themechanical attachment and the electrical contact can be madesimultaneously using a single connection method, or proceed in such away that the mechanical attachment is made first and the electricalcontact in some suitable later process stage. It is also possible toproceed in such a way that the electrical contact is made first alongwith a preliminary mechanical attachment, in which case the finalmechanical attachment is made in some suitable later process stage.

The electrical contact of the component can be made using severaltechniques:

-   -   In one embodiment, the component is connected to the conductor        layer using an ultrasonic bonding method.    -   In a second embodiment, the component is connected to the        conductor layer by soldering.    -   In a third embodiment, the component is connected to the        conductor layer by a conductive adhesive.    -   In a fourth embodiment, the component is connected to the        conductor layer using a via method.

In the first, second, and third connection techniques for the component,contact openings need not necessarily be made in the conductor layer atthe locations of the contact areas of the component. If, on the otherhand, a via method is used, contact openings, the position of whichcorresponds to the locations of the contact areas of the component, aremade in the conductor layer, or at least in the conductor-pattern partof it. The making of the contact openings too can also be performedaccording to several different embodiments:

-   -   In a first embodiment, the contact openings are made before the        attachment of the component and through the entire conductor        layer, i.e. the openings extend through both the conductor layer        and the conductor pattern. The component can then be aligned        with the contact openings.    -   In a second embodiment, the contact openings are made partly        before the attachment of the component, in such a way that the        partly made contact openings extend into the conductor layer,        without extending through it. In such an embodiment, the contact        openings are opened later to extend through the conductor        pattern, or they are opened in connection with the thinning of        the conductor layer.    -   In a third embodiment, the contact openings are made after the        attachment of the component, but before the thinning of the        conductor pattern. In such an embodiment, the contact openings        are made in such a way that they extend through the entire        conductor layer, or so that they partly penetrate it, in such a        way that they open at the latest in connection with the thinning        of the conductor layer.    -   In a fourth embodiment, the contact openings are made after the        attachment of the component and the thinning of the conductor        pattern. In such an embodiment, the contact openings extend        through the conductor layer.    -   In a fifth embodiment, the contact openings are made in the        conductor pattern in connection with the making of the conductor        pattern.

When using a via method, the contact openings are filled, in a suitablestage of the method, with a conductor material, for example, a metal,metal alloy, a conductive paste or conductive polymer, for example, aconductive adhesive. Alternatively, the edges of the contact openingsare surfaced with a conductor material. The best electrical contact isachieved using an embodiment, in which the contact openings are filledby growing metal into the openings and on top of the contact areas ofthe component, for example, using a chemical and/or electrochemicalsurfacing method. It will then be possible to create in the contactopenings a via structure that is of essentially pure metal. It will thenalso be possible to create in the contact openings a via structure,which is in metallurgical contact with the conductor material of thecontact areas.

The mechanical attachment of the component can be made using severaltechniques:

-   -   In one embodiment, the component is attached to the conductor        layer by soldering or using an ultrasonic bonding method. The        mechanical attachment created is later reinforced with the aid        of an insulating material, for example, by filling the gap        between the component and the conductor layer with a hardening        polymer, or by surrounding the component tightly with an        insulating material that adheres to the surface of both the        component and the conductor pattern.    -   In a second embodiment, the component is attached to the        conductor layer using a conductive adhesive. The adhesive can        already at the same time form itself a sufficient mechanical        attachment. The mechanical attachment can also be reinforced in        the manner described in connection with the previous embodiment.        The adhesive can be an isotropically conductive adhesive, or an        anisotropically conductive adhesive.    -   In a third embodiment, the component is attached to the        conductor layer by an insulating adhesive. An electrical contact        can be made later through the insulating adhesive.

The thinning of the conductor layer can also be performed in severaldifferent ways. The thinning of the conductor layer is intended toremoved conductor material from between the conductor patterns.

-   -   According to one embodiment, the conductor layer is thinned        throughout, in such a way that the thickness of the conductor        layer diminishes both at the locations of the conductor patterns        and in the areas remaining between the conductor patterns. The        thinning can be performed, for example, by wet-etching.    -   According to a second embodiment, the conductor layer is thinned        in areas, in such a way that the thickness of the conductor        layer diminishes in the areas remaining between the conductor        patterns, but remains essentially unchanged at the locations of        the conductor patterns. This can be achieved, for example, by        wet-etching, in which a suitable etching mask is used on the        surface of the conductor patterns.

In several embodiments, an insulating-material layer is made around thecomponent and on the surface of the conductor pattern. Theinsulating-material layer can be made from one or moreinsulating-material sheets, or from an insulating material spread in afluid form. The insulating-material layer can be made, for example,according to the following embodiments:

-   -   In one embodiment, the insulating-material layer is taken and a        conductor layer is made on its surface. Before this or after        this a suitable opening for the component is made in the        insulating-material layer.    -   In a second embodiment, an insulating-material layer is made on        the surface of the conductor layer. After this, an opening for        the component is opened in the insulating-material layer.    -   In a third embodiment, the component is first attached to the        conductor layer (mechanical attachment or electrical contact and        at least a preliminary mechanical attachment), and after this an        insulating-material layer is made on the surface of the        conductor layer and around the component.

In the embodiments, the conductor foil of the conductor layer istypically a unified, or at least a substantially unified conductor foil.Thus, there can be, for example, small holes in the conductor layer, forexample, for alignment purposes. The conductor layer can, however, behandled as a single piece. The thickness of the conductor foil istypically such that it will withstand the treatment required by theprocess without breaking or being damaged, also without support. In theembodiments, it is of course possible to use a thinner conductor foil,in which case the conductor foil will be supported with the aid of asupport layer.

In the embodiments, the conductor pattern of the conductor layerincludes conductors of the conductor-pattern layer being made in thecircuit-board structure, or patterns corresponding to these conductors.The conductors can thus be connected to each other, or separate,according to the desired circuit-board design.

References to the contact areas of the component mean conductor areas onthe surface of the component, through which an electrical contact can beformed to the component. In this meaning, the contact area can be formedby, for example, a contact bump or a conductor area on the surface ofthe component.

In the following, the invention is examined with the aid of examples andwith reference to the accompanying drawings.

FIGS. 1-8 show a series of cross-sections of the intermediate stages ofthe circuit-board structures, in a manufacturing process according to afirst embodiment.

FIGS. 9-16 show a series of cross-sections of the intermediate stages ofthe circuit-board structures, in a manufacturing process according to asecond embodiment.

FIGS. 17-22 show a series of cross-sections of the intermediate stagesof the circuit-board structures, in a manufacturing process according toa third embodiment.

FIGS. 23-26 show a series of cross-sections of the intermediate stagesof the circuit-board structures, in a manufacturing process according toa fourth embodiment.

FIGS. 27-32 show a series of cross-sections of the intermediate stagesof the circuit-board structures, in a manufacturing process according toa fifth embodiment.

In the first example, the circuit-board blank shown in FIG. 1 ismanufactured first of all. The circuit-board blank of FIG. 1 comprisesan insulating-material layer 1, a conductor foil 3 on the first surfaceof this, and a conductor foil 2 on the second surface.

The circuit-board blank also comprises a recess 4. In addition, thecircuit-board blank comprises a thinner insulating-material layer 11between the insulating-material layer 1 and the conductor foil 2. Theinsulating-material layer 11 can be of material differing from that ofthe insulating-material layer 1, or it can be part of theinsulating-material layer 1. In the former case, the circuit-board blankof FIG. 1 may have been formed, for example, by laminating together orotherwise combining with each other the insulating-material layer 1, theconductor foil 2, the conductor foil 3, and the insulating-materiallayer 11. In the latter case, the circuit-board blank of FIG. 1 may havebeen formed, for example, in such a way that a recess 4 has been made inthe blank formed by the insulating-material 1, the conductor foil 2, andthe conductor foil 3. In that case, the recess 4 will not extentcompletely through the insulating-material layer 1, but instead acorresponding part of the insulating-material layer 11 has been left onthe ‘bottom’ of the recess.

The method of the example can, of course, be modified in such a way thatthe recess 4 extends to the conductor foil 2, in which case there willnot be an insulating-material layer 11 in the circuit-board blank, atleast at the location of the recess. However, at least in someembodiments the reliability of the circuit-board structure can beimproved by using an insulating-material layer 11. This is due to thefact that the use of an insulating-material layer 11 for its partensures that unnecessary openings will not remain in the insulatingmaterial between the component and the conductor foil 2.

Manufacture continues from the situation shown in FIG. 1, by spreadingresist layers 5, typically photoresist layers, on the surfaces of theconductor foils 2 and 3. This stage is shown in FIG. 2. The photoresistlayers 5 are exposed through a patterned mask and after this the blankis developed. After developing, the exposed photoresist layers 5 arepatterned in the desired manner to form conductor-pattern masks, whichis shown in FIG. 3.

Manufacture is continued by electrolytically growing a conductormaterial, typically copper, in the areas from which the photoresist wasremoved. The desired conductor patterns 6 and 7 are then formed on thesurfaces of the conductor foils 2 and 3, which is shown in FIG. 4. Thethickness of the conductor pattern can be, for example, 20 micrometreswhile the width of the line of the conductor patterns being made can beless than 20 micrometres. The method can thus also be used tomanufacture small and precise conductor patterns.

The method can be modified in such a way that a layer of some othermetal or metal alloy, for example tin, can be made on the surface of theconductor patterns 6 and 7, or on the interface between the conductorfoils 2 and 3 and the conductor patterns 6 and 7. This layer can be usedas an etching stop.

The method can also be modified in such a way that the recess 4 is madeonly after the spreading of the photoresist layer 5, or at an even laterprocess stage.

After the manufacture of the conductor patterns 6 and 7, the resistlayers 5 can be removed. In addition, contact openings 8 are made in theconductor pattern 6 of the circuit-board blank, at the locations of thecontact areas of the component. The contact openings 8 can be made insuch a way that they essentially extend through the conductor pattern 8,or in such a way that they essentially extend through both the conductorpattern 8 and the conductor foil 2, (i.e. through the entire conductorlayer). It is also possible to make the contact openings from the otherdirection, in such a way that they extend through only theinsulating-material layer 11 and the conductor foil 2. In the example,the contact openings 8 are made in such a way that they extend throughthe conductor pattern 6, the conductor foil 2, and theinsulating-material layer 11. FIG. 4 shows the circuit-board blank afterthis intermediate stage.

The contact openings 8 can be made, for example, by drilling with alaser. The contact openings 8 are aligned correctly in position relativeto the conductor pattern 6. The mutual position of the contact openings8 corresponds to the mutual position of the contact areas of thecomponent. Thus, at least one contact opening 8 is made for each contactarea participating in the creation of an electrical contact. The surfacearea of the contact openings 8 being made can be more or less as largeas the surface area of the corresponding contact areas. The surface areaof a contact opening 8 can, of course, also be selected to be smaller,or in some embodiments slightly larger, than the surface area of thecorresponding contact area.

In the example, the component 9 is attached to the circuit-board blankwith the aid of an adhesive 10. For the gluing, an adhesive layer 10 isspread on the surface of the insulating-material layer 11, on the‘bottom’ of the recess 4. FIG. 5 shows this intermediate stage.Alternatively, the adhesive layer can be spread on the attachmentsurface of the component 9, or on both the attachment surface of thecomponent 9 and on the surface of the insulating-material layer 11. Theadhesive 10 can also be spread in stages and in layers. After this, thecomponents 9 can be aligned in the positions designed for the components9, with the aid of alignment marks. For example, the contact openings 8,or the conductor patterns 6 or 7, or separate alignment marks (not shownin the figures) can act as alignment marks. FIG. 6 shows thecircuit-board blank after the gluing of the component 9.

The term attachment surface of the component 9 refers to that surface ofthe component 9 that will face the conductor pattern 6. The attachmentsurface of the component 9 comprises contact areas, by means of which anelectrical contact can be made to the component. The contact areas canbe, for example, flat areas on the surface of the component 9, or moreusually contact protrusions, such as contact bumps, on the surface ofthe component 9. There are usually at least two contact areas or contactprotrusions in the component 9. In complex microcircuits there can wellbe many contact areas.

In many embodiments, it is advantageous to spread so much adhesive onthe attachment surface or attachment surfaces that the adhesivecompletely fills the space between the component 9 and the structurecoming against the component. A separate filler agent will then not berequired. Good filling will reinforce the mechanical connection betweenthe component 9 and the circuit-board blank, so that a mechanically moredurable construction will be achieved. A comprehensive adhesive layer 10without gaps will also support the conductor pattern and protect thestructure in later process stages. During gluing, adhesive also usuallygets into the contact openings 8, if these open towards the attachmentsurface.

The term adhesive refers to a material, by means of which a componentcan be attached to the circuit-board blank. One property of an adhesiveis that the adhesive can be spread on the surface of the circuit-boardblank and/or of the component in a relatively fluid form, or otherwisein a form that conforms to surface shapes, for example, in the form of afilm. Another property of an adhesive is that after spreading theadhesive hardens or can be hardened, at least partly, so that theadhesive will be able to hold the component in place at least until thecomponent is attached to the structure in some other way. The thirdproperty of the adhesive is its adhesive ability, i.e. its ability tobond to the surface being glued.

The term gluing refers to attaching the component and the circuit-boardto each other with the aid of an adhesive. In gluing, adhesive is thusbrought between the component and the circuit-board blank and thecomponent is set in a suitable position relative to the circuit-boardblank, in which the adhesive is in contact with the component and thecircuit-board blank and at least partly fills the space between thecomponent and the circuit-board blank. After this, the adhesive isallowed to (at least partly) harden or the adhesive is (at least partly)actively hardened, so that the component attaches to the circuit-boardblank with the aid of the adhesive. In some embodiments, the contactprotrusions of the component may, during gluing, extend through theadhesive layer to come in contact with the rest of the structure of thecircuit-board blank.

The adhesive used in the embodiments is, for example, a thermally curedepoxy. The adhesive is selected in such a way that the adhesive used hassufficient adhesion with the circuit-board blank and the component. Oneadvantageous property of the adhesive is a suitable coefficient ofthermal expansion, so that the thermal expansion of the adhesive willnot differ too much from the thermal expansion of the surroundingmaterial during the process. The adhesive selected should alsopreferably have a short hardening time, preferably of a few seconds atmost. In this time the adhesive should harden at least partly in such away that it is able to hold the component in place. The final hardeningcan take clearly more time and the final hardening can indeed bedesigned to take place in connection with later process stages. Theelectrical conductivity of the adhesive is preferably in the order ofthe electrical conductivity of insulating materials.

The component 9 to be attached can be, for example, an integratedcircuit, such as a memory chip, a processor, or an ASIC. The componentto be attached can also be, for example, a MEMS, LED, or a passivecomponent. The component to be attached can be cased or uncased, and itcan comprise contact bumps in the contact areas or be without bumps.There can also be a conductor surfacing thinner than a contact bump onthe surface of the contact areas of the component. The outer surface ofthe contact areas of the component can thus be on the level of the outersurface of the component, on the bottom of recesses on the surface ofthe component, or on the surface of protrusions extending from thesurface of the component.

After the gluing of the component 9, the recess is filled with a fillermaterial 12. The example can also be modified in such a way thatmanufacture is started from a circuit-board blank (the situation in FIG.1), which comprises only a conductor foil 2 and possibly aninsulating-material layer 11. After this, process stages that areotherwise the same as those described above, except that naturally themethod stages relating to the conductor foil 3, the conductor pattern 7,and the resist layer 5 relating to them are omitted. In this embodiment,the circuit-board blank comprises, after the gluing of the component(refer to FIG. 6):

-   -   a conductor layer formed by a conductor foil 2 and a conductor        pattern 6,    -   an adhesive layer 10,    -   optionally an insulating-material layer 11 between the conductor        layer and the adhesive layer 10,    -   contact openings 8, and    -   at least one component 9.

In this modified embodiment, there is not recess 4 to be filled, insteadin this stage an insulator layer 1, which surrounds the component 9 andsupports the conductor layers 2 and 6, is made on the surface with thecomponent 9 of the circuit-board blank. The insulator layer 1 can beformed, for example, by putting an insulating-material sheet, in whichopenings have been made at the location of the components 9, on top onthe circuit-board blank. In addition, a unified insulating-materialsheet can be put on top of the insulating-material sheet 9. Both sheetscan be similar, or sheets than differ from each other can also be used,at least one of which is prehardened or unhardened. Examples ofmaterials suitable for the insulator layer 1 are PI (polyimide), FR4,FR5, aramid, polytetrafluoroethylene, Teflon®, LCP (liquid crystalpolymer), and a prehardened binder layer, i.e. prepreg. Theinsulating-material sheets put on top of the circuit-board blank arepressed, with the aid of heat and pressure, to form a unified insulatorlayer 1. In the insulating-material sheets, on the upper surface of onecan also be a ready conductor-pattern layer, so that after pressing thecircuit-board blank comprises at least two conductor-pattern layers, asshown by the series of figures. In this embodiment, conductor patterns 7can, however, also be designed at the location of the components 9.

Both in the example shown in the figure series and in the abovedescribed modification, it is next possible to make vias 13, with theaid of which electrical contacts are made between the contact areas ofthe components 9 and the conductor patterns 6. For the making of vias,the contact openings 8 are cleaned of adhesive and other materials thatmay have been pushed into them. In connection with the cleaning of thecontact openings 8, it is also possible to clean the contact areas ofthe components 9, thus further improving the preconditions for making ahigh-quality electrical contact. The cleaning can be performed using,for example, a plasma technique, chemically, or with the aid of a laser.If the contact openings 4 and the contact areas are already sufficientlyclean, the cleaning can naturally be omitted.

If the contact openings 8 were made to only partly penetrate, thecontact openings 8 are opened in this stage. It is also possible toproceed in such a way that the contact openings 8 are made entirely inthis stage.

After cleaning, it is also possible to examine the success of thealignment of the component 9, as the contact areas of a correctlyaligned component will be visible through the contact openings 8, whenviewed from the direction of the conductor pattern.

After this, a conductor material is introduced to the contact openings8, in such a way that it forms an electrical contact between thecomponent 9 and the conductor pattern 6. The conductor material of thevias 13 can be made, for example, by filling the contact openings 8 withan electrically conductive paste. The conductor material can also bemade using one of several growing methods known in the circuit-boardindustry. High-quality electrical contacts can be made, for example, byforming a metallurgical connection by growing a conductor material usinga surfacing method, for example, a chemical or electrochemical method.One good alternative is the growing of a thin layer using a chemicalmethod and continuing the growing using a more economicalelectrochemical method. The term filling refers to the fact that thecontact openings are at least substantially filled with the conductormaterial. Instead of filling, surfacing can also be performed in such away that only the edges of the contact openings are surfaced. Inaddition to these methods, it is of course possible to also use someother method, which will be beneficial in terms of the end result.

In the example of the figure series, the contact openings 8, the contactareas of the component 9, and the conductor patterns 6 are surfacedfirst of all with a thin conductor layer and then afterwards thethickness of the conductor layer is increased electrolytically until thecontact openings 8 are filled with conductor material. FIG. 7 shows thestructure after the growing. After this, the circuit-board blank isetched, to remove the excess conductor material. If a protectivemembrane is used on the surface of the conductor patterns 6 and 7, theconductor material is removed essentially only from those parts of theconductor foils 2 and 3 that remain outside the conductor patterns 6 and7. Alternatively, it is possible to etch the entire conductor layer, sothat the material of the conductor foils 2 and 3 is removed from outsidethe conductor patterns 6 and 7. In that case, material of the conductorpatterns 6 and 7 too will be removed, but the conductor patterns 6 and 7will be copied into the material of the conductor foils 2 and 3.

The series of FIGS. 9-16 shows one variation of the examples describedabove. In the variation, the suitable parts of the method stagesdescribed above are utilized and the procedure is as follows:

-   -   A circuit-board blank is made, which comprises an insulator        layer 1, a recess 4, and conductor foils 2 and 3 (FIG. 9).    -   Photoresists 5 are spread and exposure takes place through the        masks (FIG. 10). The exposed areas 5′ are shown darkened in the        figure.    -   Contact openings 8 are made (FIG. 11).    -   Adhesive 10 is spread (FIG. 12).    -   The component 9 is attached to the circuit-board blank with the        aid of an adhesive layer 10 (FIG. 13) and the recess 4 is filled        with a filler agent 12.    -   The resist is developed, so that all that remains are the        unexposed areas of the resist 5. The contact openings 8 are        cleaned. The circuit-board blank after these stages is shown in        FIG. 14.    -   Conductor material is grown using an electrolytic method. The        conductor material then grows in the openings of the resist 5        and the contact openings 8 are filled, thus forming both        conductor patterns 6 and 7 and vias 13 (FIG. 15).    -   The resist 5 is removed and the conductor material is etched, so        that the desired conductor pattern is separated from the        conductor layer when the conductor material is removed from the        areas between the conductor patterns (FIG. 16).

In the embodiment shown in the series of FIGS. 9-16 the conductor foils2 and 3 are preferably thin relative to the conductor patterns 6 and 7to be grown on their surfaces. The conductor foils 2 and 3 are thusintended to conduct the current required by the electrolytic growing tothe growing areas. If the conductor foils 2 and 3 are thin relative tothe conductor patterns 6 and 7, the etching of the conductor foils 2 and3 away from outside the conductor patterns 6 and 7 will notsubstantially affect the relative dimensions of the conductor patterns 6and 7.

The series of FIGS. 17-22 shows a third variation of the examplesdescribed above. In the variation, suitable parts of the method stagesdescribed above are utilized and the procedure is as follows:

-   -   A circuit-board blank is made, which comprises a conductor foil        2 and a conductor pattern 6 (FIG. 17). This can be made, for        example, in such a way that a resist 5, which is exposed and        developed, is spread on top of the conductor foil 2. After this,        metal is grown in the openings formed in the resist 5, for        example, using an electrochemical method. In this variation,        contact openings are also defined in the exposure mask of the        resist, so that the resist will remain at the locations of the        contact openings 8′. Thus, in connection with the growing of the        conductor pattern 6, contact openings 8 are also formed in the        conductor patterns 6, and are thus aligned directly and in a        self-aligning manner in the correct places relative to the        conductor pattern 6.    -   The resist is removed and the contact openings 8 are opened to        also extend through the conductor foil 2 (FIG. 18).    -   The component 9 is glued onto the surface of the conductor        pattern 6 with the aid of an adhesive 10 (FIG. 19). The        component is aligned in the correct position relative to the        conductor pattern 6 and the contact openings 8.    -   An insulating-material layer 1 is made on top of the        circuit-board blank (FIG. 20).    -   The contact openings 8 are cleaned and vias 13 are made in the        contact openings from a conductor material (FIG. 21). In the        example of the figure, the vias 13 are made using a surfacing        method. In that case, the vias are surfaced in such a way that        the necessary electrical contact arises, i.e. generally a        conductor layer is made at least on the edges of the contact        openings 8. In the example of the figure, the contact openings 8        are grown full of the conductor material. The more conductor        material is put into a via 13, the better will be the        conductivity of the via 13. The vias 13 are indeed preferably        made to be at least substantially filled with conductor        material.    -   The conductor foil 2 is removed, for example, by etching (FIG.        22).

The series of FIGS. 23-26 shown a fourth variation of the examplesdescribed above. In the variation, suitable parts of the method stagesdescribed above are utilized and the procedure is as follows:

-   -   A circuit-board blank is made, which comprises a conductor foil        2 and a conductor pattern 6 (FIG. 23). This can be made, for        example, in such a way that a resist 5, which is exposed and        developed, is spread on top of the conductor foil 2. After this,        metal is grown in the openings formed in the resist 5, for        example, using an electrochemical method.    -   A component 9 is glued on top of the conductor pattern 6, with        the aid of an anisotropically conductive adhesive 20 (FIG. 24).        The anisotropically conductive adhesive 20 forms an electrical        contact in the direction between the contact areas of the        component and the conductor pattern 6. The adhesive 20 is,        however, electrically insulating in the transverse direction, so        that an electrical contact is not formed between the contact        areas of the component, nor between the separate conductors of        the conductor pattern 6.    -   An insulating-material layer 1 is made on top of the        circuit-board blank and on the surface of that a conductor foil        3 (FIG. 25).    -   The conductor foil 2 is removed, for example, by etching. The        conductor foil 3 is patterned to form a conductor pattern 7        (FIG. 26).

The series of FIGS. 27-32 shows a fifth variation of the examplesdescribed above. In the method, suitable parts of the method stagesdescribed above are utilized, and the procedure is as follows:

-   -   A circuit-board blank is made, which comprises a conductor foil        2 and a conductor pattern 6 (FIG. 27). This can be made, for        example, in such a way that a resist 5, which is exposed and        developed, is spread onto top of the conductor foil 2. After        this, metal is grown in the openings formed in the resist 5, for        example, using an electrochemical method.    -   A second resist 15, which is exposed and developed, is spread on        top of the resist 5 and conductor pattern 6. A conductor        material is made in the opening formed in the resist 15, for        example, using an electrochemical method. The made conductor        areas form contact bumps 17 on the surface of the conductor        pattern 6 (FIG. 28).    -   The resists 5 and 15 are removed (FIG. 29).    -   A component 9 is attached on top of the conductor pattern 6 and        against the contact bumps 17, using a suitable method (FIG. 30).        In the example of the figure, the joint is made by an ultrasonic        bonding method or alternatively by a thermo-compression bonding        method. In the example of the figure, a component 9 is used,        which does not itself contain contact bumps.    -   An insulating-material layer 1 is made on top of the        circuit-board blank, and a conductor foil 3 of top of that (FIG.        31).    -   The conductor foil 2 is removed, for example, by etching. The        conductor foil 3 is patterned to form a conductor pattern 7        (FIG. 32).

In the embodiments, it is possible to also use a separate support layerto support the conductor foil, or the conductor layer formed by theconductor foil and the conductor pattern.

A suitable intermediate layer, which will not dissolve in the etchingagent used, or will dissolve in it extremely slowly, can also be usedbetween the conductor foil and the conductor pattern, or on the surfaceof either of them. Thus the etching stops at the intermediate layer andthe desired surface can be defined precisely. An intermediate layer ofthis kind can be made, for example, from some other metal, such as tin.If necessary, the intermediate layer can be removed, for example,chemically with some other etching agent.

When using a manufacturing method, in which the contact openings 8 arealigned and made after the manufacture of the conductor pattern 6, thesensitivity of the method to alignment errors can be reduced bydimensioning the diameter of the contact openings 8 to be greater thanthe width of the conductors of the conductor pattern 6.

There are numerous variations of the methods according to the examplespresented above while the methods depicted by the examples can also becombined with each other. The variations can relate to individualprocess stages, or to the mutual sequence of the process stages.

Many features, which do not appear in the previous examples, can also bemanufactured into the circuit-board structure. For example, in additionto vias that participate in the creation of electrical contacts, thermalvias can also be made, which are intended to conduct heat moreefficiently away from the component 9. The increase in the efficiency ofheat conducting is based on the thermal conductivity of the thermal viabeing greater than that of the insulating material surrounding thecomponent. As electrical conductors are typically also good thermalconductors, the thermal vias can in most cases be made using the sametechnique and even in the same process stage as the electrical contactsto the components 9.

On the basis of the previous examples, it is obvious that the method canalso be used for manufacturing many different kinds of three-dimensionalcircuit structures. The method can be used, for example, in such a waythat several components, for example, semiconductor chips, are placed ontop of each other, thus forming a packet containing several components,in which the components are connected to each other to form a singlefunctional totality. Such a packet can be termed a three-dimensionalmulti-chip module.

The examples of the figures depict some possible processes, with the aidof which our invention can be exploited. However, our invention is notrestricted to only the processes described above, but instead theinvention covers various other processes too and their end products,within the full scope of the Claims and taking equivalenceinterpretation into account. The invention is also not restricted toonly the structures and methods described by the examples, but insteadit will be obvious to one versed in the art that various applications ofour invention can be used to manufacture very many different kinds ofelectronic modules and circuit boards, which may even differ greatlyfrom the examples presented. Thus the components and circuits of thefigures are presented only with the intention of illustrating themanufacturing process. Many alterations can be made to the processes ofthe examples described above, while nevertheless not deviating from thebasic idea according to the invention. The alterations can related, forexample, to the manufacturing techniques depicted in the various stages,or to the mutual sequence of the process stages.

With the aid of the invention, it is also possible to manufacturecomponent packets for attachment to a circuit board. Such packets canalso contain several components, which are connected electrically toeach other.

The method can also be used to manufacture entire electrical modules.The module can also be a circuit board, to the outer surface of whichcomponents can be attached, in the same way as to a conventional circuitboard.

1. A method for manufacturing a circuit-board structure, the methodcomprising: providing a conductor foil; spreading a resist layer on theconductor foil; patterning the resist layer to form a conductor-patternmasks having openings for conductor patterns; growing a conductorpattern on top of the conductor foil in the openings of theconductor-pattern masks; attaching a component to the conductor foil andconductor pattern; removing the conductor material of the conductor foilfrom outside the conductor pattern.
 2. A method according to claim 1,wherein the resist layer is a photoresist layer.
 3. A method accordingto claim 1, further comprising; adding a layer of a metal or metal allyon the surface of the conductor pattern or on the interface between theconductor foil and the conductor pattern.
 4. A method according to claim1, wherein the conductor foil is provided on an insulating materiallayer.
 5. A method according to claim 4, further comprising; forming arecess in the conductor foil and insulating material layer compositionafter spreading the resist layer.
 6. A method according to claim 1,further comprising; removing the resist layer after the growth of theconductor pattern.
 7. A method according to claim 1, further comprising;forming contact openings in the conductor pattern.
 8. A method accordingto claim 7, wherein the contact openings are formed through theconductor pattern and the conductor foil.
 9. A method according to claim4, further comprising; forming contact openings in the insulatingmaterial layer and the conductor foil.
 10. A method according to claim9, wherein the formation of the contact openings in the insulatingmaterial layer and the conductor foil does not form contact openings inthe conductor pattern.
 11. A method according to claim 10, furthercomprising; opening contact openings in the conductor pattern layercorresponding to the formed contact openings in the insulating materiallayer and the conductor foil.
 11. A method according to claim 4, whereinthe conductor foil and insulating material layer composition has arecess, and wherein the component is attached to the circuit boardstructure within the recess.
 12. A method according to claim 12, furthercomprising; applying a sufficient amount of adhesive to both attach thecomponent to the circuit board structure and completely fill the spacebetween the component and the structure coming against the component.13. A method according to claim 12, further comprising; filling therecess with a filler material.
 14. A method according to claim 1,further comprising; forming an insulator layer, which surrounds thecomponent and supports the conductor pattern, on the surface of thecircuit board structure with the component.
 15. A method according toclaim 14, wherein the formation of the insulator layer is the additionof a sheet of insulating material with a premade opening at the locationof the component to the circuit board structure.